1. Field of the Invention
The invention pertains to the field of diagnostic x-ray imaging, including among other things, techniques for generating images representative of structures within an object.
2. Description of Related Art
Real-time x-ray imaging is increasingly being required by medical procedures as therapeutic technologies advance. For example, many electro-physiologic cardiac procedures, peripheral vascular procedures, PTCA procedures (percutaneous transluminal catheter angioplasty), urological procedures, and orthopedic procedures require the use of real-time x-ray imaging. In addition, modern medical procedures often require the use of instruments, such as catheters, that are inserted into the human body. These medical procedures often require the ability to discern accurately locations of instruments that are inserted within the human body, often in conjunction with an accurate image of the surrounding body through the use of x-ray imaging.
A number of real-time x-ray imaging systems are known. These include fluoroscope-based systems where x-rays are projected into an object to be imaged, and shadows caused by relatively x-ray opaque matter within the object are displayed on a fluoroscope located on the opposite side of the object from the x-ray source. However, such systems have great difficulty forming images that distinguish particular structures or regions within the depth of the object to be imaged (i.e., where the image is "focused" upon particular structures or regions of interest within the object). This is due in part to the geometry of such fluoroscope-based systems, in which the x-ray opaque properties of the entire depth of the object contributes to the final image, regardless of the exact depth of specific x-ray opaque structures/regions within the object.
One approach to generating an image of particular structures or regions within an object is provided by computed tomography ("CT") imaging systems. In operation, CT systems perform multiple x-ray projections or x-ray measurements of the object to be imaged from multiple angles. The data from the multiple projections can be manipulated to construct an image of a particular plane/slice within the object. Multiple image planes/slices can be made a various depths within the object by moving the CT imaging system and the object relative to each other. However, conventional CT systems are not able to generate a focussed image of at particular structure within an object if the structure of interest lies across multiple image planes/slices at various depths within the object.
Another approach to x-ray imaging involves the use of reverse-geometry x-ray imaging systems. In such systems, an x-ray tube is employed in which an electron beam is generated and focussed upon a small spot on a relatively large target assembly, emitting x-ray radiation from that spot. The electron beam is deflected in a scan pattern over the target assembly. A relatively small x-ray detector is placed at a distance from the target assembly of the x-ray tube. The x-ray detector converts x-rays that strike it into an electrical signal indicative of the amount of x-ray flux detected at the detector. One advantage provided by reverse-geometry systems is that the geometry of such systems allows x-rays to be projected at an object from multiple angles without requiring physical relocation of the x-ray tube. However, the particular x-ray detector used in such systems often limits the spatial resolution of such systems, thereby limiting the quality/range of images that can be obtained. Moreover, known reverse-geometry x-ray imaging systems do not have the functionality to generate a focussed image of structures at various depths within an object.
Therefore, it is desired to create an imaging system that can generate an accurate representation of internal structures within an object.